Brushless motor with magnetic sensor to detect leaked magnetic flux

ABSTRACT

A brushless motor includes a stator and a rotor rotatably supported inside the stator. The rotor has a rotor yoke formed by laminating a large number of steel plates, the rotor yoke has an even number of magnetic pole portions protruding outward, and a field magnet is fitted to each of the magnetic pole portions or every other magnetic pole portions. A magnetic sensor is disposed within the range in which the sensor can directly detect a magnetic flux leaking outside from an end face of the rotor and is less affected by irregular fluxes near the rotor end face, so that this sensor can detect a peak point of a flux density around the rotor. A magnetic sensor is disposed within the range where the influences of the irregular fluxes are small. A magnet to be detected is fitted to the rotor end face, and a magnetic sensor for one direction and a magnetic sensor for the other direction are disposed near the trajectory of rotation of the detected magnet.

CROSS-REFERENCE TO THE RELATED APPLICATIONS

This is a continuing application of Ser. No. 08/757,339 filed Nov. 27,1996, now abandoned, and Ser. No. 08/362,518 filed Mar. 20, 1995, nowabandoned.

TECHNICAL FIELD

This invention relates to a brushless motor which has a rotor havingfield permanent magnets inserted into a rotor yoke made of laminatedsteel plates and a magnetic sensor disposed to oppose to the end face ofthe rotor.

BACKGROUND ART

Generally known conventional brushless motors consist of a rotor whichhas a plurality of field permanent magnets inserted into a rotor yokemade of laminated steel plates, and a stator which has a magnetic poleportion opposed to the outer peripheral face of the magnet portion ofthe rotor with a small gap therebetween.

This type of brushless motor is proposed, to detect a rotationalposition of the rotor, to adhere to an end face of the rotor a magnetpiece to be detected for specifying a rotational position of the rotor,to dispose a magnetic sensor near the trajectory of rotation of themagnet piece to be detected, and to use the magnetic sensor to detectmagnetism of the magnet piece to be detected, thereby detecting therotational position of the rotor.

FIG. 37 shows a vertical sectional view of the above brushless motorhaving the magnet pieces. A brushless motor 51 has a pair of housingmembers 53, 54 fastened with bolts 52, and these housing members 53, 54rotatably support a rotatable shaft 57 with ball bearings 55, 56. To therotatable shaft 57, a rotor 58 is fixed, and one end of the rotatableshaft 57 is structured to protrude from the end face of the housingmember 53 to externally transmit a rotary force of the rotor 58. Astator 59 is disposed around the rotor 58 and held between the housingmembers 53, 54.

The rotor 58 consists of a rotor yoke 50 which has many steel plateslaminated, and a plurality of field permanent magnets 61 which areinserted into the rotor yoke 50. The stator 59 consists of a stator yoke62 made of laminated steel plates, and stator coils 63 wound on thestator yoke 62. A part of the inner peripheral face of the stator yoke62 forms a magnetic pole portion 59a of the stator, and the statormagnetic pole portion 59a is opposed to the outer peripheral face of amagnetic pole portion 58a of the rotor 58 with a small distancetherebetween.

A magnet piece 64 to be detected is adhered to an end face 58b of therotor 58. A magnetic sensor board 66 having a plurality of magneticsensors 65 disposed is fixed to the housing member 53 near thetrajectory of rotation of the magnet piece 64 to be detected.

In the above structure, when the rotor 58 of the brushless motor 51rotates, the magnet piece 64 to be detected is also rotated andapproached to the magnetic sensors 65 when it is rotated 360 degrees.The magnetic sensors 65 detect magnetism of the magnet piece 64 to bedetected to detect the rotational position of the rotor 58. But, it isknown that since this brushless motor 51 has a large distance betweenthe field permanent magnets 61 and the stator magnet pole portion 59a, amagnetic flux is attracted in the rotating direction by an interactionwith the stator magnetic pole portion 59a when rotating, and theposition of a magnetic flux density peak point in an outside space ofthe rotor 58 does not agree with the actual rotational position of therotor 58.

FIG. 38 shows a difference between a change of the magnetic flux densityin the outside space of the rotor end face 58b of the brushless motor 51and the rotational position of the rotor 58 detected by the magnet piece64 to be detected. In FIG. 38, the horizontal axis shows a lapse oftime, and the vertical axis shows the magnitude of an electric signal.Curve L1 shows a change of the magnetic flux density in the outsidespace of the rotor end face 58b, and kinked line L2 shows the rotationalposition of the rotor 58 detected by the magnet piece 64 to be detected.It is seen from the drawing that in a brushless motor having fieldpermanent magnets in a rotor yoke and a relatively large distancebetween the field permanent magnets and a stator magnetic pole portion,a magnetic flux during rotation is attracted in the rotating directionby the stator magnetic pole portion, and the magnetic flux density(curve L1) forms a waveform advanced than the actual rotational position(kinked line L2) of the rotor. Specifically, the alternate long andshort dash line indicates a state that the magnetic flux density (curveL1) is not advanced than the actual rotational position (kinked line L2)of the rotor, but the magnetic flux density (curve L1) indicated by thesolid line is advanced by a time difference T at the position of point 0of the electric signal than the magnetic flux density (curve L1)indicated by the alternate long and short dash line. This timedifference T can be converted into a rotational angle of the rotor, andthis rotational angle is equal to the displacement of the magnetic flux.And it is known that this displacement of the magnetic flux (hereinafterreferred to as an angle of lead) increases substantially in proportionto the magnitude of a current applied to the motor.

Regarding the deviation of the position of the magnetic flux densitypeak point in the outside space of the rotor 58 from the actualrotational position of the rotor 58, when a Hall IC is used, a rotatingspeed is fixed at 1200 rpm, and torque is varied, the deviation of thepeaks of the magnetic flux density outside of the rotor and the signalof the Hall IC obtained from the magnet to be detected at the maximumefficiency with respective torque is as follows.

    ______________________________________               Deviation of Hall IC and    Torque     peaks of magnetic flux                              Maximum    (Kgm)      density (electrical angle)                              efficiency (%)    ______________________________________    0.05         20° ± 10°                              90    0.10       22.5° ± 10°                              87    0.15         25° ± 10°                              85    0.20       28.5° ± 9°                              82    0.25        30° ± 9°                              79    ______________________________________

As obvious from the above table, the peak point of the magnetic fluxdensity in the space around the rotor 58 is advanced than the actualrotational position of the rotor 58. Further, this angle of lead isalmost proportional to the motor torque, and an attaching error of theHall IC to obtain the maximum efficiency is in a range of 20° (±10°),but a tolerance becomes small as the torque increases, making itdifficult to attach.

FIG. 39 is a magnetic sensor board of a three-phase four-pole brushlessmotor. In this case, a Hall IC was used for the magnetic sensor. A HallIC 65 is one IC combining a function of detecting the direction of amagnetic field using the Hall effect and the function of an amplifier.When N pole is approached to above the Hall IC, output is about 5 (V),and when S pole, output is 0 (V). Therefore, one cycle of an electricalangle becomes N (5V) and S (0V), but since one cycle of a mechanicalangle becomes N, S, N and S, it is known that the electrical angle tothe mechanical angle is 2 to 1. (The electrical angle will behereinafter referred to as the "electrical angle", and the mechanicalangle will not be indicated.)

Generally, the three-phase four-pole brushless motor needs three HallICs 65 at intervals of 60 degrees peripherally on a circle having thesame diameter (a distance R from the center axis is 23 mm in thisexample, which will be simply referred to as "R23" hereinafter), andthey are soldered at intervals of 60 degrees on the magnetic sensorboard 66. Furthermore, mounting holes 67 are formed at two locations ofthe magnetic sensor board 66 to fix to the housing member, and a pattern69 is not formed on a peripheral portions 68 around the mounting holes67. Lands 70 are disposed as connections to drive the Hall ICs 65 or toexternally output a signal, and a through hole 71 is formed at thecenter of each land 70. A lead 72 is inserted in the through hole 71from the back of the magnetic sensor board 66 and soldered on the land70. The magnetic sensor board 66 has an outer periphery 73 to locateinside the coil 63 and an inner periphery 74 to locate outside the outerperiphery of the housing bearing. And, an angle in the rotatingdirection is in a shape that a size for the mounting holes 67 is addedto an arranging angle of 120 degrees for the three Hall ICs, so that thepattern is closely formed although the magnetic sensor board has a largeshape.

Since the above conventional brushless motor detects only the rotationalposition of the rotor using the magnet piece to be detected, it hasdisadvantages that an angle of lead of the magnetic flux which variesdepending on the motor current or motor torque cannot be detected, andwhen the magnetic pole portion of the stator is excited based on thedetected signal, the stator magnetic pole portion which generates arotary force most cannot be excited, and the motor efficiency islowered.

On the other hand, it is considered to dispose the magnet piece to bedetected or the magnetic sensor previously displaced in one directionassuming the angle of lead a magnetic flux, but this method cannot beapplied to a bidirectionally rotatable brushless motor which is requiredto rotate the rotor in both directions.

While the above method detects the rotational position of the rotor yokeby the above magnetic sensor, there is a known sensorless brushlessmotor which detects the rotational position of the rotor by utilizing aback electromotive force to be generated on the stator side by therotation of the rotor.

This sensorless brushless motor can detect the highest position of themagnetic flux density around the rotor, but has a disadvantage that anelectric circuit is complicated because the back electromotive forcegenerated on the stator side is detected.

SUMMARY OF THE INVENTION

Accordingly, an object of this invention is to provide a brushless motorhaving a rotor which has a plurality of field permanent magnets insertedinto a rotor yoke made of steel plates laminated in many numbers, which,in a simple structure, can detect the peak point of a magnetic fluxdensity with respect to an angle of lead of the magnetic flux variabledepending on the motor current, and has a high motor efficiency(brushless motor of a first group).

Another object of this invention is, in the above type of brushlessmotor, to provide in a simple structure a brushless motor which candetect the peak point of a magnetic flux density with respect to anangle of lead variable depending on the motor torque and has a highmotor efficiency, and to provide a brushless motor whose cost is reducedby miniaturizing a magnetic sensor board and improving a fixing method(brushless motor of a second group).

Still another object of this invention is, in the above type ofbrushless motor, to provide in a simple structure a bidirectionallyrotatable brushless motor which can detect the peak point of a magneticflux density around the rotor when rotating in either direction, and hasa high motor efficiency (brushless motor of a third group).

Other objects of this invention are to provide a small number of devicescapable of improving the performance of the above brushless motors.

The brushless motor of the first group according to this invention, in abrushless motor comprising a stator and a rotor rotatably supportedwithin the stator, the rotor having a rotor yoke which is formed bylaminating many steel plates, the rotor yoke having an even number ofmagnetic pole portions protruded outward, and a field permanent magnetwhich is inserted in each magnetic pole portion or every other magneticpole portions, is characterized by having a magnetic sensor fordetecting a magnetic flux leaked outside from an end face of the rotor,the magnetic sensor being positioned at a prescribed distance from theend face of the rotor, the prescribed distance being in a range of adistance or less that the magnetic sensor can directly detect themagnetic flux leaked outside from the end face of the rotor and also adistance or more that a noise is generated in a detected signal due toirregular magnetic fluxes near the end face of the rotor.

Therefore, the brushless motor of this invention has the magnetic sensordisposed at the prescribed distance from the end face of the rotor todirectly detect the magnetic flux leaked outside of the rotor end facethrough the rotor yoke, so that a position of the peak point of themagnetic flux density around the rotor can be detected even when themagnetic flux of the rotor is attracted toward the rotating direction bythe interaction with the stator when rotating. Thus, an optimum magneticpole portion of the stator can be excited according to the position ofthe peak point of the magnetic flux density around the rotor, and abrushless motor having a high motor efficiency regardless of the angleof lead of the magnetic flux can be obtained.

And, in the brushless motor of this invention, the magnetic sensor candirectly detect the magnetic flux from the field permanent magnets ofthe rotor and is disposed at the distance so as not to be largelyaffected by irregular magnetic fluxes near the rotor end face, largelyreducing noises in an electric signal showing the rotational position ofthe rotor. And, the magnet piece to be detected required in conventionalbrushless motors can be omitted to provide a brushless motor having asimple structure.

In this specification, the magnetic sensor is used in a sense includinga coil. Therefore, the coil is included in a concept of the magneticsensor not only in the invention of the first group but also through thefollowing description.

The brushless motor of the second group according to this invention, ina brushless motor comprising a stator and a rotor rotatably supportedwithin the stator, the rotor having a rotor yoke which is formed bylaminating many steel plates, the rotor yoke having an even number ofmagnetic pole portions protruded outward, and a field permanent magnetwhich is inserted in each magnetic pole portion or every other magneticpole portions, is characterized by having a magnetic sensor fordetecting a magnetic flux leaked outside from an end face of the rotor,setting a radial distance of the magnetic sensor from the center of arotatable shaft to scan a range outside of the field magnets and insideof the outer end of the rotor, disposing a plurality of magnetic sensorson circles having different diameters on a magnetic sensor board, andarranging a pitch interval of each magnetic sensor on the circledifferent from a pitch interval of a stator winding phase.

And, the brushless motor of the second group according to thisinvention, in a brushless motor comprising a stator and a rotorrotatably supported within the stator, the rotor having a rotor yokewhich is formed by laminating many steel plates, the rotor yoke havingan even number of magnetic pole portions protruded outward, a fieldpermanent magnet which is inserted in each magnetic pole portion orevery other magnetic pole portions, and a plurality of magnetic sensorsto detect a magnetic flux leaked outside from an-end face of the rotor,is characterized by a method for disposing the magnetic sensors that theplurality of magnetic sensors are disposed on circles having differentdiameters to advance a rotor detecting position, a rotational angle ofthe magnetic sensors is adjusted to delay the angle of lead, and a spacebetween the magnetic sensors is narrowed.

Therefore, since the above brushless motor of this invention disposesthe magnetic sensors at a prescribed distance from the end face of therotor to directly detect the magnetic flux of the field permanentmagnets leaked outside from the rotor end face by the magnetic sensors,when the magnetic flux of the rotor during rotating is attracted in therotating direction by the interaction with the stator magnetic poleportion or the angle of lead is varied due to the motor current (motortorque), the position of the peak point of the magnetic flux density inthe outside space of the rotor is always detected to excite an optimummagnetic pole portion of the stator, and the motor efficiency can beimproved. Further, since a change in the maximum efficiency against amounting error of the magnetic sensors in the rotating direction is lessand the angle of lead is same regardless of the load, setting can bemade under any load.

And, the method for disposing the magnetic sensors according to thisinvention can vary a distance of the magnetic sensors from the shaft tochange the angle of lead and narrow the angle between the magneticsensors. As a result, the size of the magnetic sensor board is reducedand its cost is lowered.

The brushless motor of the third group according to this invention, in abrushless motor comprising a stator and a rotor rotatably supportedwithin the stator, the rotor having a rotor yoke which is formed bylaminating many steel plates, the rotor yoke having an even number ofmagnetic pole portions protruded outward, and a field permanent magnetwhich is inserted in each magnetic pole portion or every other magneticpole portions, is a bidirectionally rotatable brushless motor which ischaracterized by attaching a magnet piece to be detected to an end faceof the rotor to specify a rotational position of the rotor, anddisposing a one direction magnetic sensor for detecting a rotationalposition of the rotor rotating in one direction and an other directionmagnetic sensor for detecting a rotational position of the rotorrotating in the other direction in the vicinity of the trajectory ofrotation of the magnet piece to be detected, the one direction magneticsensor and the other direction magnetic sensor being displacedrespectively by a prescribed angle substantially equal to the angle oflead of a magnetic flux in opposite directions with respect to arotating direction of the rotor to detect a desired position of therotor.

Therefore, the bidirectionally rotatable brushless motor of thisinvention has a magnet piece to be detected for specifying a rotationalposition of the rotor, a magnetic sensor for detecting a rotationalposition of the rotor rotating in one direction and a magnetic sensorfor detecting a rotational position of the rotor rotating in the otherdirection, and since these magnetic sensors are fixed as displaced by aprescribed angle almost equal to an angle of lead of a magnetic flux inopposite directions with respect to a rotating direction of the rotor,when the rotor is rotating, the magnetic sensors output the rotationalposition of the rotor advanced by the angle of lead of the magnetic fluxthan the actual rotational position of the rotor. This outputtedrotational position of the rotor agrees with the peak point of amagnetic flux density in the outside space of the rotor, so that therotor can be rotated most efficiently by exciting the magnetic poleportion of the stator based on the output.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1! A vertical sectional view showing one embodiment of thebrushless motor of this invention.

FIG. 2! A view showing the front of the rotor of the brushless motor ofthis invention.

FIG. 3! A perspective view showing a magnetic flux outside of the rotorend face of the brushless motor of this invention.

FIG. 4! Graphs showing the compared analogue waveforms of magnetism witha distance D between the magnetic sensor and the rotor end face varied.

FIG. 5! A vertical sectional view of the brushless motor of thisinvention with a nonmagnetic plate adhered to the rotor end face.

FIG. 6! Graphs showing the compared analogue waveforms of magnetism of abrushless motor having a nonmagnetic plate and a brushless motor nothaving a nonmagnetic plate.

FIG. 7! A front view showing a rotor of the brushless motor of thisinvention.

FIG. 8! A magnetic sensor board diagram of the three-phase four-polebrushless motor of this invention.

FIG. 9! A graph showing the relation between an angle of lead and adistance from the shaft center of a Hall IC.

FIG. 10! A graph showing the relation between a distance from the shaftcenter of a Hall IC and a moving angle of the Hall IC for obtaining themaximum efficiency.

FIG. 11! A side view of the Hall IC and the rotor end face of thisinvention.

FIG. 12! A side view of the Hall IC and the rotor end face of anotherembodiment of this invention.

FIG. 13! A view showing the front of a rotor of the brushless motor ofanother embodiment of this invention.

FIG. 14! A vertical sectional view showing another embodiment of thebrushless motor of this invention.

FIG. 15! A sectional view taken on line A-A' of FIG. 14.

FIG. 16! A table showing the results of measuring the relation betweenthe radial position and the efficiency of the Hall IC.

FIG. 17! A graph showing the performance when the Hall IC is at aposition of R23 mm.

FIG. 18! A graph showing the performance when the Hall IC is at aposition of R21 mm.

FIG. 19! A view showing a magnetic sensor board.

FIG. 20! A block diagram of an electronic circuit.

FIG. 21! A view showing a magnetic sensor board and part of a stator.

FIG. 22! A sectional view showing a brushless motor and a fixing memberfor fixing it.

FIG. 23! A view showing a magnetic sensor board.

FIG. 24! A sectional view of a magnetic sensor board.

FIG. 25! A view showing a magnetic sensor board using a sheet coil.

FIG. 26! A view showing a magnetic sensor board having toroidal windingsapplied.

FIG. 27! A flowchart showing the control of a motor rotation.

FIG. 28! A view partly showing a magnetic sensor and a rotor.

FIG. 29! A graph showing the relation between an angle of lead and adistance between a magnetic sensor 16 and a rotor end face 8b.

FIG. 30! A graph showing the relation between a positional change of amagnetic sensor and a rotation speed and torque.

FIG. 31! A graph showing the relation between a Hall voltage and amagnetic flux density.

FIG. 32! A graph showing the relation between a magnetic flux densityand a temperature.

FIG. 33! A view showing an output voltage waveform of a magnetic sensorwith a rotor rotated.

FIG. 34! A view showing a rotor end face.

FIG. 35! A perspective view showing a rotor.

FIG. 36! A vertical sectional view showing a brushless motor with abuilt-in fan.

FIG. 37! A vertical sectional view showing a conventional brushlessmotor.

FIG. 38! A graph showing a difference between a change of the

magnetic flux density of a conventional brushless motor and the detectedrotational position of the rotor.

FIG. 39! A view showing the magnetic sensor board of a conventionalthree-phase four-pole brushless motor.

BEST MODE FOR CARRYING OUT THE INVENTION

A first embodiment of the invention will be described with reference tothe drawings.

FIG. 1 shows a vertical sectional view of the brushless motor of thisembodiment. A brushless motor 1 has a pair of housing members 3, 4fastened with bolts 21 and these housing members 3, 4 rotatably supporta rotatable shaft 7 with ball bearings 5, 6. To the rotatable shaft 7, arotor 8 is fixed, and one end of the rotatable shaft 7 is structured toprotrude from the end face of the housing member 3 to externallytransmit a rotary force of the rotor 8. A stator 9 is disposed aroundthe rotor 8 and held between the housing members 3, 4.

The rotor 8 consists of a rotor yoke 10 which has many steel plateslaminated, and a plurality of field permanent magnets 11 which areinserted into the rotor yoke 10. The stator 9 consists of a stator yoke12 made of laminated steel plates, and stator coil$13 wound on thestator yoke 12. A part of the inner face of the stator yoke 12 forms amagnetic pole portion 9a of the stator 9, and the magnetic pole portion9a of the stator is opposed to the outer peripheral face of a magneticpole portion 8a of the rotor 8 with a small distance therebetween. Thestator coil 13 is connected to an external power supply through a lead14a.

A magnetic sensor 16 such as a Hall element and a Hall IC is attached toa part of the housing member 3 opposing to the end face 8b of the rotor8. The magnetic sensor 16 and the rotor end face 8b are opposed to eachother with a prescribed distance D therebetween. Reference numeral 14bindicates an electric signal lead for externally sending an electricsignal of magnetism detected by the magnetic sensor 16.

FIG. 2 shows an end face of the rotor 8. The rotor 8 consists of fourrotor magnetic pole portions 8a protruded outward in the radialdirection at an angle of 90 degrees, and the field permanent magnet 11inserted into each rotor magnet pole portion 8a. At the center of therotor 8, the rotatable shaft 7 is inserted, and the rotatable shaft 7and the rotor 8 are configured to rotate integrally with a key 7a.Reference numeral 18 indicates caulking sections for integrally caulkingthe Δ steel plates which form the rotor yoke 10.

Each field permanent magnet 11 is inserted in the base of the rotormagnetic pole portion 8a so that N and S poles are alternatelypositioned outside. The magnetic flux of the field permanent magnets 11is guided by the leading end of the rotor magnetic pole portion 8a, andgets in or out of the outer peripheral face of each rotor magnetic poleportion 8a. Thus, the field permanent magnets 11 of the rotor 8 arealternately magnetized in the N and S poles in the circumferentialdirection.

Imaginary lines A, A' in the drawing indicate the trajectories where themagnetic sensor 16 is relatively moved by the rotation of the rotor 8.On the other hand, imaginary lines B, B' and a hatched area αtherebetween indicate an unstable area of the magnetic flux present onthe outer periphery of the rotor 8. The magnetic flux in the unstablemagnetic flux area α is always varied unstably by an effect of therotating magnetic field generated by the stator 9. As shown in thedrawing, the relative moving trajectories A, A' of the magnetic sensor16 are positioned outside of the field permanent magnets 11 and insideof the unstable magnetic flux area α.

And, as shown in FIG. 2, the rotor 8 has a groove M between the rotormagnetic pole portions 8a, and the bottom M0 of the groove M issubstantially aligned with the relative trajectories of rotation A, A'of the magnetic sensor 16. The trajectories A, A' where the magneticsensor 16 moves pass near the intersection of the base ends of the rotormagnetic pole portions 8a, and irregular magnetic fluxes to be describedafterward are present near the intersection of the base ends of therotor magnetic pole portions 8a, tending to be a cause to generate anoise in the detected electric signal.

FIG. 3 shows a relation between the position of the magnetic sensor andthe irregular magnetic fluxes near the intersection of the magnetic poleportions 8a.

In the space on the outer periphery of the rotor 8, there is a magneticflux indicated by code W0 which gets out from the leading end face ofthe rotor magnetic pole portion 8a having N pole and reaches the leadingend face of the rotor magnetic pole portion 8a having S pole. On theother hand, at the end face of the rotor, there is a magnetic fluxindicated by code W1 which continues from N pole to S pole of the fieldpermanent magnets 11. And, between the adjacent rotor magnetic poleportions 8a, there is a magnetic flux W2 which gets out from the endface of the leading end of the rotor magnetic pole portion 8a having Npole and reaches the leading end face of the rotor magnetic pole portion8a having S pole. As shown in FIG. 3, this magnetic flux W2 passes anirregular route which separates from the rotor end face 8b, approachesto the rotor end face 8b and separates again to reach the leading end ofthe neighboring rotor magnetic pole portion 8a having S pole. Thisirregular magnetic flux W2 has a large irregularity when being close tothe rotor end face 8b, and a magnetic flux W3 separated from the rotorend face 8b has a smooth shape like a parabola.

The magnetic sensor 16 of this embodiment is disposed at a position toseparate from the rotor end face 8b in such a degree that it does notcross the above irregular magnetic flux W2 and to approach the rotor endface 8b in such a degree that it crosses the above smooth-shapedmagnetic flux W3.

In this case, a gap between the above irregular magnetic flux W2 and theparabola magnetic flux W3 is largest at the bottom M0 of the groove M ofthe rotor 8, and the bottom M0 of the groove is substantially alignedwith the relative trajectories of rotation A, A' of the magnetic sensor16. Therefore, it is most convenient for the magnetic sensor 16 todetect a noiseless detection signal

The action of this embodiment will be described based on the abovestructure.

The magnetic sensor 16 of this embodiment is positioned outside of theirregular magnetic flux W2 between the field permanent magnets 11 andcrosses the smooth-shaped magnetic flux W3, so that it can detect aposition of the peak point of the magnetic flux density around the rotor8 without producing a noise by an effect of an irregular portion of themagnetic flux.

FIG. 4 shows the comparison of analogue signals of magnetism detected bythe magnetic sensor 16 with a distance D between the magnetic sensor 16and the rotor end face 8b varied. In FIGS. 4(a), (b), (c) and (d) show alapse of time on the horizontal axis with respect to brushless motorshaving a distance D of 2 mm, 3 mm, 4 mm and 4.9 mm, respectively. Theirregular uneven spots indicated by points a0, a1 in FIG. 4 (a) show theeffect of the irregular magnetic flux W2 between the above fieldpermanent magnets 11. The irregular uneven spots of the analogue signalsof magnetism become a noise in the electric signal when converted into adigital signal. When this noise is large, the stator magnetic poleportion 9a cannot be excited appropriately, and the rotor 8 cannot berotated smoothly.

It is clear by comparing FIG. 4 (a) to FIG. 4 (d) that the irregularuneven spots of the analogue signal of magnetism decreases as thedistance D increases, detection can be made when the distance D is about4 mm or more, and as shown in FIG. 4 (d), when the distance D is about4.9 mm, the analogue signal of magnetism by the magnetic sensor 16 showsa smooth sine curve and is converted into a digital signal without manynoises.

When the rotor 8 rotates in the direction R shown in FIG. 3, magneticfluxes W0, W1, W2, W3 of the rotor 8 are attracted toward the directionR' shown in the same drawing by the interaction with the stator magneticpole portion 9a. The angles of lead of the magnetic fluxes W0, W1, W2,W3 relate to the motor current or torque, and it is known that the angleof lead is increased as the motor current is increased. In thisembodiment, the magnetic sensor 16 directly detects the magnetic fluxdensity in the external space of the rotor end face 8b, so that theposition of a peak point of the magnetic flux density can be detected.Thus, the stator magnetic pole portion 9a optimum to generate a rotaryforce most corresponding to the peak point of the magnetic flux densitycan be excited, and the motor efficiency can be improved.

In this embodiment, when the brushless motor was operated using a Hallelement as the magnetic sensor under conditions of a distance D of 4.9mm, a rotating speed of 1200 rpm and torque of 0.24 kgm, the motorefficiency was improved by about 10% as compared with a conventionalbrushless motor having a magnet piece to be detected.

This embodiment can also use a Hall IC as the magnetic sensor. The HallIC is one IC combining a function of detecting the direction of amagnetic field using the Hall effect and the function of an amplifier.When N pole is approached to above the Hall IC, output is about 5 (V),and when S pole, output is 0 (V), thus it is a detecting elementresistant to an electrical noise. When the Hall IC is used as themagnetic sensor, the motor efficiency can be improved by setting thedistance D smaller than in using the Hall element by virtue of ahysteresis property of the Hall IC. The motor efficiency of thebrushless motor using the Hall IC as the magnetic sensor underconditions of a rotating speed of 1200 rpm and torque of 0.24 kgm withthe distance D varied is shown below.

    ______________________________________    Distance between    magnetic sensor and    rotor end face                  Motor current                             Motor efficiency    D (mm)        (A)        (%)    ______________________________________    5.3           5.57       74.9    4.4           5.08       78.5    3.4           4.88       80.0    2.9           4.88       80.0    2.3           4.88       80.0    ______________________________________

It is seen from the above that detection can be made when D is 2.3 mm ormore, and 2.3-3.4 mm is optimum because the motor efficiency is stable.

On the other hand, when a brushless motor having a magnet piece to bedetected was operated under the same conditions, a motor current of7.40A and a motor efficiency of 63.2% were obtained. Specifically, usingthe brushless motor 1 of this embodiment using the Hall IC, the motorefficiency could be improved by up to about 17%.

Attachment of a nonmagnetic plate to the rotor end face can also reducea magnetic noise.

FIG. 5 shows a vertical sectional view of a brushless motor having anonmagnetic plate attached to the rotor end face. Components same asthose in FIG. 1 are given the same reference numerals and theirdescription is omitted. In this embodiment, a nonmagnetic plate 8c madeof stainless steel is adhered to the rotor end face 8b of a brushlessmotor 1. The adhesion of the nonmagnetic plate 8c to the rotor end face8b converts a part of the magnetic flux leaked outside from the rotorend face 8b into an eddy current, so that the magnetic flux getting outof the nonmagnetic plate 8c has a smooth route as the whole. Since theroute of the magnetic flux is smoothed, the analogue waveform ofmagnetism detected by the magnetic sensor 16 is smoothed, and convertedinto a digital signal without many noises.

FIG. 6 shows graphs of compared analogue waveforms detected by eachmagnetic sensor of a brushless motor having the nonmagnetic plate 8c anda brushless motor not having it.

FIG. 6 (a) shows analogue waveforms of magnetism of the brushless motorwithout the nonmagnetic plate, while FIG. 6 (b) shows analogue waveformsof magnetism of the brushless motor having the nonmagnetic plate adheredto the rotor end face. The horizontal axis in FIG. 6 shows time which isgraduated in 5 ms, and three curves respectively correspond to analoguewaveforms of U, V and W phases of the motor. In FIG. 6 (a), points Nshow an effect by irregular magnetic fluxes. These irregular analoguewaveforms N make noises when converted into a digital signal. On theother hand, FIG. 6 (b) shows that the above irregular magnetic fluxesare converted into an eddy current by the nonmagnetic plate 8c, formingrelatively smooth analogue waveforms, and a digital signal without manynoises can be obtained.

In the above embodiment, the nonmagnetic plate 8c is adhered to therotor end face 8b, but the nonmagnetic plate 8c may be positionedbetween the magnetic sensor 16 and the rotor end face 8b. For example,the nonmagnetic plate 8c may be attached to the surface of the magneticsensor 16. Furthermore, addition of alumina material to the nonmagneticplate 8c makes it easy to externally transmit the heat of the magnet,thereby contributing to prevent the thermal demagnetization of themagnet.

In the above description, the rotor has the field permanent magnets 11inserted into the base of each rotor magnetic pole portion 8a. But, itis to be understood that this invention is not limited to the above butalso applied to a rotor that the field permanent magnet is inserted intoevery other rotor magnetic pole portions so as to have the magnetic poleportions of alternate N and S poles in the circumferential direction bythe repulsion of mutual field permanent magnets.

As obvious from the above description, according to the brushless motorof the first group of this invention, the magnetic sensor is disposed ata prescribed distance from the end face of the rotor to directly detectthe magnetic flux of the field permanent magnets leaked outside from therotor end face by the magnetic sensor, so that when the magnetic flux ofthe rotor during rotation is attracted in the rotating direction by theinteraction with the magnetic pole portions of the stator or the angleof lead of the magnetic flux is varied depending on the motor current,the position of a peak point of the magnetic flux density in theexternal space of the rotor is always detected to excite the optimummagnetic pole portion of the stator, so that the motor efficiency can beimproved. And, by the same action, the optimum stator magnetic poleportion can be excited by the magnetic sensor in the brushless motorwhich rotates in both directions.

And, according to the brushless motor of this invention, the magneticsensor is positioned outside of the irregular magnetic flux between thefield permanent magnets of the rotor, and to cross the smooth-shapedmagnetic flux, so that a noise due to the irregular magnetic fluxes canbe reduced, and the magnet piece to be detected which has been requiredheretofore can be omitted, enabling to obtain a simple-structuredbrushless motor.

Now, the brushless motor of the second group of this invention will bedescribed.

The brushless motor of the second group basically has the same structurewith the one shown in FIG. 1 and, therefore, the same components aregiven the same reference numerals and their description is omitted. Inthe brushless motor of the first group, the space between the rotor endface and the magnetic sensor has been considered. On the other hand, inthe brushless motor of the second group, the positional relation of themagnetic sensor in a radial direction will be mainly considered.

FIG. 7 shows an end face 8b of the rotor 8 of this invention. The rotor8 consists of rotor magnetic pole portions 8a protruded outward in theradial direction at an angle of 90 degrees, and the field permanentmagnets 11 inserted into the rotor magnet pole portions 8a. The fieldpermanent magnet 11 has its length in its axial direction equal to orshorter than the length of the rotor 8, and the magnet end face ispositioned at least the inside of the rotor end face 8b on the magneticsensor side. When the magnet end face is protruded from the rotor endface, the magnetic sensor cannot detect a leaked magnetic flux, and aspace between the rotor end face 8b and the magnetic sensor cannot bekept. Furthermore, it is revealed that the rotor end face 8b ispreferably equal to or longer than the stator end face 9b because theleaked magnetic flux is increased and easily detected. At the center ofthe rotor 8, the rotatable shaft 7 is inserted, and the rotatable shaft7 and the rotor 8 are integrally fixed by shrinkage fitting.

The field permanent magnets 11 are inserted in the bases of the rotormagnetic pole portions 8a so that N and S poles are alternatelypositioned to face outside. The magnetic flux of the field permanentmagnets 11 is guided by the leading end of the rotor magnetic poleportion 8a, and gets in or out of the outer peripheral face of eachrotor magnetic pole portion 8a. In this structure, the magnetic poleportions 8a of the rotor 8 are alternately magnetized in the N and Spoles in the circumferential direction. An area between imaginary linesA-B in the figure (in this case, a distance R from the center axis isfrom 21 mm to R23 mm.) indicate an area that when a top 19a of themagnetic sensor 16 (in this case, a Hall IC) enters this area by therotation of the rotor 8, the leaked magnetic flux from the rotor endface is detected and the motor can be driven. This imaginary line B isgenerally located on a circle with a radius which is at the midpointbetween the outer wall of the field magnet 11 and the outer end of therotor 8 regardless of the size of the motor.

On the other hand, an area between imaginary lines B-C in the drawing(in this case, a distance from the center axis is from R23 mm to R26mm.) indicates an unstable area of the leaked magnetic flux present onthe outer periphery of the rotor 8. The leaked magnetic flux in theunstable area is constantly varied unstably by an effect of a rotatingfield generated by the stator 9, and although the motor rotates, themotor efficiency at the operation range of low rotation and low torqueresults in inferior by about 4% than in the trajectory A-B. Furthermore,an area between imaginary lines A-D (in this case, a distance from thecenter axis is from R8 mm to R21 mm.) indicates an unstable area presenton the inner periphery of the rotor 8. In the leaked magnetic flux inthis unstable area, a magnetic flux between the field permanent magnetsis hardly leaked and attracted by a magnetic field generated by thestator 9 in the groove M0, making a switching section of the magneticflux unstable. Thus, the motor cannot be rotated.

In the drawing, an imaginary line E indicates a limit line that themagnetic sensor can driven normally when a bottom 19b of the magneticsensor (Hall IC) 16 is outside of the imaginary line E. And, when thecaulking sections 18 are between the imaginary lines E and D, the leakedmagnetic flux from the rotor end face can be correctly detected but,when the caulking sections 18 are outside of the imaginary line E, theleaked magnetic flux from the rotor end face becomes unstable due to theunevenness of the caulking sections, and particularly the switchingsection of the magnetic flux becomes unstable. Therefore, a signal ofthe magnetic sensor cannot be adopted.

As shown in the drawing, by setting the top 19a of the magnetic sensor(Hall IC) 16 in the area A-B of the rotor and the caulking sections 18inside the imaginary line E, a stable magnetic flux can be obtained, andstable efficiency and rotation can be obtained.

In the above embodiment, as the range that the magnetic sensor 16 candetect the leaked magnetic flux from the rotor end face and the motorcan be driven, the area between the imaginary lines A-B in FIG. 7 hasbeen taken, and the specific numerical values "21 mm" and "23 mm" havebeen shown to indicate that the area A-B is an area with a distance Rfrom the center axis is from 21 mm to R23 mm. The above description doesnot mean that the area A-B is not limited to the above numerical values.More specifically, the area A-B as an area that the motor can be drivenis to be understood in a relative positional relation between the outerdiameter (about R26 mm) of the rotor 8 and the field permanent magnets11. And, when a vertical line is assumed from the center axis to thefield permanent magnet 11, it is revealed that the line A indicatesalmost the outer wall of the field permanent magnet 11 and the line Bindicates almost the middle of the line A in the above assumed verticalline and the rotor outer end. These positions are generally appropriatepositions whatever size the motor shape may have.

And, when the Hall IC is set to the above position (R23 mm), a rotatingspeed is fixed at 1200 rpm, and torque is varied, the deviation of thepeaks of the magnetic flux density outside of the rotor and the signalof the Hall IC obtained from the rotor end face at the maximumefficiency with respective torque is as follows.

    ______________________________________               Deviation of Hall IC and    Torque     peaks of magnetic flux                              Maximum    (Kgm)      density (electrical angle)                              efficiency (%)    ______________________________________    0.05       10° ± 15°                              90    0.10       10° ± 15°                              87    0.15       10° ± 15°                              85    0.20       10° ± 15°                              82    0.25       10° ± 15°                              79    ______________________________________

It is seen from the above table that when torque is 0.05 Kgm forexample, it is necessary to make the deviation of a signal of the HallIC and the peak of the magnetic flux density outside the rotor 10°±15°(electrical angle) to obtain the maximum efficiency 90% and, similarly,when torque is 0.10 Kgm, it is necessary to make the deviation of asignal of the Hall IC and the peak of the magnetic flux density outsidethe rotor 10°±15° (electrical angle) to obtain the maximum efficiency87% (the same as above).

As obvious from the above table, when the position of the magneticsensor board is set at a low load point (e.g., the above 0.05 Kgm) bydirectly detecting the leaked magnetic flux from the rotor end face, themaximum efficiency can be obtained under respective loads, the maximumefficiency has less change with respect to the mounting error of theHall IC in the rotating direction, and the deviated degree is sameregardless of the load, so that setting can be made under any load.

Specifically, when the rotor 8 rotates, the magnetic flux of the rotormagnetic pole portion is attracted by the interaction with the statormagnetic pole portion. This angle of lead relates to the motor currentor torque, and the angle of lead is increased as the motor current isincreased (as the torque is increased). And, the Hall IC directlydetects the magnetic flux in the external space of the rotor end face8b, so that the stator magnetic pole portion 9a optimum to generate arotary force most corresponding to the peak point of the magnetic fluxdensity can be excited, and the motor efficiency can be improved.

FIG. 8 is a view showing a magnetic sensor board 15 of the three-phasefour-pole brushless motor of this invention. In this embodiment, a HallIC is used for the magnetic sensor.

Assuming that the rotor is rotated clockwise, a Hall IC 16a (the top endof the Hall IC is R23 mm from the center axis in this embodiment), aHall IC 16b (R22 mm form the center axis in this embodiment) and a HallIC 16c (R21 mm from the center axis in this embodiment) are set atdifferent distances from the center axis at intervals of 52 degrees inthe peripheral direction and displaced inward toward the rotatingdirection of the rotor, and soldered for fixing. Furthermore, two shaftmounting holes 21 for fixing the magnetic sensor board 15 to the statorare disposed at the outer end of the magnetic sensor board. A land 24 isapplied around the mounting holes 21, and the land 24 has a thick copperfoil to retain a sufficient mechanical strength after inserting a shaftand soldering or fixing with a resin. Furthermore, C-shaped lands 20 aredisposed as connections to drive the Hall ICs or to externally output asignal, a lead 14b can be easily inserted vertically and horizontally inthe magnetic sensor board, and the lands 20 have partly a wide area toallow soldering. The lead 14b is a flat cable having a one-bodyinsulator for lines, so that it can be quite easily inserted in aC-shaped material such as the lands 20.

The magnetic sensor board 15 has a size such that its outer periphery 25is positioned inside the stator coil 13 and its inner periphery 23 canbe positioned arbitrarily. In other words, since the magnetic sensorboard is fixed using the outer periphery, it is not necessary to use theinner periphery as the reference to fix to the housing member. And, theboard can be made broad toward the outer diameter of the rotatable shaft7. As a result, a pattern 22 can be formed easier, an insulated spacebetween the patterns can be secured sufficiently, it is not necessary todraw the pattern outside of the lands 20, and the lands 20 can be formedin an open type like a letter C. Furthermore, since the angle in therotating direction is sufficient in a size between the pitches of theHall IC as described afterward, the size of the magnetic sensor board 15becomes very compact and its production cost is low.

FIG. 9 shows the variation of an angle of lead when the Hall IC 16 ismoved outward from the shaft center with a position of R21 mm from theshaft center as the reference. FIG. 10 shows a moving angle of the HallIC in the rotating direction to obtain the maximum efficiency when theHall IC is moved outward with R21 mm from the shaft center as thereference.

In FIG. 8 to FIG. 10, determining an angle in the rotating direction ofthe rotor to be (+) and an angle in the counter-rotating direction ofthe rotor to be (-), when the Hall IC is simply moved outward from R21mm to R23 mm, the rotor detection position is proportionally on theadvancing side because a magnetic flux close to the stator, which is aleaked magnetic flux to be attracted, is picked up as seen in FIG. 9.But, after passing R23 mm, an advancing degree tends to decreasegradually because the shape of the magnetic pole portion is limited.And, when the Hall IC is moved outward from R21 mm to R26 mm, the angleof lead is excessive, deviating the position of the maximum efficiencyof the angle of lead, and the motor efficiency is lowered. But, as seenin FIG. 10, it was experimentally found that when the Hall IC was movedto the (-) side, the maximum efficiency was obtained at respectivepositions and the obtained maximum efficiencies were substantially notdifferent. When the Hall IC is at R20.5 mm or below or R26.5 mm or morefrom the shaft center, the motor does not rotate. Therefore, theapplicable areas in the drawing are hatched.

With the Hall IC 16c (R21 from the shaft center) as the reference, theHall IC 16b (R22 from the shaft center) is positioned normally at anangle of 60 degrees. As shown in FIG. 9, when the position is 1 mmoutside from the shaft center, the electrical angle advances by 15degrees. On the other hand, as shown in FIG. 10, when the rotationalangle of the Hall IC is moved, the same maximum efficiency can beobtained, and 60°-8°=52° becomes an angle between the Hall IC 16c andthe Hall IC 16b. Similarly, an angle (52°) is obtained between the HallIC 16b and the Hall IC 16a. As a result, a distance between the Hall ICscould be narrowed by 16° as compared with prior art, and the magneticsensor board 15 could be made compact.

FIG. 11 is a side view of the Hall IC and the rotor end face. To detecta magnetic flux leaked from the magnetic pole portion 8a in the outsidespace of the rotor 8, the magnetic sensor (Hall IC) 16 disposed on themagnetic sensor board 15 is directed toward the rotor end face 8b, and aspace between the rotor 8 and the magnetic sensor board 15 is adjustedwith a stepped shaft 28. More specifically, one end 28a of the shaft 28is inserted into the mounting hole 21 of the magnetic sensor board in adirection Q and soldered on a land side 15a. Another end 28b is forcedinto the stator magnetic pole portion (not shown) and fixed. The spacebetween the rotor end face and the Hall IC is adjusted according to asize L1 of the shaft 28. In this embodiment, when the axial distancebetween the rotor end face and the Hall IC is less than 2.3 mm, manymagnetic fluxes leak from the rotor end face, so that normal operationcannot be made. Therefore, the size L1 is set to be 2.3 mm or more.

And, it was experimentally found about the magnetic flux that athickness of the field permanent magnet is proportionally related withthe space between the rotor end face and the Hall IC. Specifically, asthe field permanent magnet becomes thicker, the leaked magnetic fluxfrom the field permanent magnet increases and, even if the Hall IC isseparated from the rotor end face, sensing can be made. Furthermore, thelead 14b is inserted into the land 20 from a top face P of the magneticsensor board 15 and fixed by soldering or with a resin.

FIG. 12 is a side view showing another embodiment of the Hall IC and therotor end face. In this case, the magnetic sensor board 15 and themagnetic sensor (Hall IC) 16 are disposed to face opposite from theabove embodiment. The space between the rotor 8 and the magnetic sensorboard 15 is adjusted according to a size L2 of the stepped shaft 28, andthe mounting space of the Hall IC is equal to the size L2. Furthermore,since the shaft end 28a is inserted in the opposite direction andsoldering is made in the opposite direction, or the land side 15a isfaced to the opposite direction from the end face 8b, soldering to theland side 15a is made easy.

And, the lead 14b is soldered as it is on a wide area of the land 20,and the soldered face and every parts such as the Hall IC are positionedon the land side 15a, making it easy to produce. To a counter-land side15b, a shield sheet 29 is affixed to prevent a noise of the board frommixing with a noise of the leaked magnetic flux from the rotor end face.Therefore, the magnetic flux free from a noise can be fully detected bythe Hall IC. Thus, the adhesion of the shield sheet 29 to thecounter-land side allows to externally output a stable signal and alsoto measure a magnetic flux near by about 30% to the rotor end face ascompared with the ordinary space between the rotor end face and thesensor board without providing the shield sheet 29.

FIG. 13 shows another embodiment of the rotor end face.

A rotor 30 consists of rotor magnetic pole portions 30b radiallyprotruded at an angle of 90 degrees and field permanent magnets 31inserted into rotor magnetic pole portions 30a. At the center of therotor 30, a rotatable shaft 32 is inserted, and the rotatable shaft 32and the rotor 30 are integrally fitted by shrinkage fitting.

Each field permanent magnet 31 is inserted in the bases of every othermagnetic pole portions 30a so that N pole (or S pole) is positioned onthe rotatable shaft side. The magnetic fluxes of the field permanentmagnets 31 are guided by the leading ends of the magnetic pole portions30a to get in or out of the outer peripheral face of each rotor magneticpole portion 30b. Thus, the rotor 30 is alternately magnetized in the Nand S poles in the circumferential direction. An area between imaginarylines B-C in the drawing (in this case, a distance from the center axisis from R23 mm to R26 mm) indicates an area that when a top 33 of a HallIC 32 enters this area by the rotation of the rotor 30, a magnetic fluxswitching section becomes stable and the motor can be driven.

Furthermore, an area between imaginary lines B-D (in this case, adistance from the center axis is from R8 mm to R23 mm) indicates an areathat the rotor 30 is unstable. In this area, the magnetic fluxes of themagnetic pole portions having the field permanent magnet and not havinghave different movements, the magnetic flux switching section becomesunstable and the motor cannot be driven.

In the above description, a magnetic sensor signal has been explained tobe taken from the magnetic flux leaked from the rotor end face, but thisinvention is not limited to it. When rare earth magnets having a highenergy product (BHMAX25MGOe) are inserted in the rotor to cause magneticsaturation at one spot at a minimum on the rotor end face and a magneticflux is leaked intentionally on the outside of the rotor, a quantity ofmagnetism which flows the magnetic sensor is increased, and detectioncan be made satisfactorily even when the magnetic sensor has variationsin the property. In particular, when the magnetic saturation is close toa place where poles are switched, detention can be made stably at a spotliable to be unstable. Furthermore, it is to be understood thatreliability of the motor is improved and assembling is facilitated byincreasing the axial distance between the magnetic sensor and the rotorend face.

As obvious from the above description, according to the brushless motorof the second group of this invention, the magnetic sensor is disposedat a prescribed distance from the end face of the rotor to directlydetect the magnetic flux of the field permanent magnets leaked outsidefrom the rotor end face by the magnetic sensor, so that when themagnetic flux of the rotor during rotation is attracted in the rotatingdirection by the interaction with the magnetic pole portions of thestator or the angle of lead of the magnetic flux is varied depending onthe motor current (motor torque), the position of a peak point of themagnetic flux density in the external space of the rotor is alwaysdetected to excite the optimum magnetic pole portion of the stator, sothat the motor efficiency can be improved. In addition, the maximumefficiency has less change with respect to the mounting error of theHall IC in the rotating direction, and the angle of lead is sameregardless of the load, so that setting can be made under any load.

And, since the magnetic sensor board of this invention has the mountingholes for fixing the sensor board disposed at the outer periphery, theinner periphery of the sensor board can be widened to the rotatableshaft, the insulated space between the patterns can be securedsufficiently, and the shape of the connection land with the lead can bechanged. As a result, the lead can be easily inserted and connected.And, changing of the distance of the Hall IC from the shaft changes theangle of lead, and the angle between the Hall ICs can be narrowed. As aresult, the size of the magnetic sensor board can be made small, and thecost can be reduced.

The brushless motor of the third group of this invention will bedescribed.

As shown in FIG. 14, the brushless motor of the third group basicallyhas the same structure with the one shown in FIG. 1 and, therefore, thesame components are given the same reference numerals and theirdescription is omitted.

In FIG. 14, to an end face 8b of the rotor 8, a magnet piece 17 to bedetected is attached to specify a rotational position of the rotor 8. Tothe inner end face of the housing member 3 near the trajectory ofrotation of the magnet piece 17 to be detected, a CW magnetic sensor 16(16X) for detecting a rotational position of the rotor 8 rotatingclockwise and a CCW magnetic sensor 16 (16Y) for detecting a rotationalposition of the rotor 8 rotating counterclockwise are attached.

FIG. 15 shows the front of the rotor 8 taken on line A-A' shown in FIG.14. The rotor 8 consists of the rotor yoke 10 made of the laminatedsteel plates and the field permanent magnets 11, and the rotor yoke 10has four externally protruded sections in a radial direction at an angleof 90 degrees on its outer periphery. These four protruded sections ofthe rotor yoke 10 have the field permanent magnet 11 inserted in theirbases so that N and S poles are alternately positioned to face outwardto respectively form the rotor magnetic pole portion 8a. In the drawing,reference numeral 18 indicates caulking sections for integrally caulkingthe steel plates.

At the center of an end face of one of the rotor magnetic pole portions8a, the magnet piece 17 to be detected is adhered. This magnet piece 17to be detected moves along the trajectory of rotation R when the rotor 8rotates clockwise CW or counterclockwise CCW as shown in FIG. 15. To anend face of the housing member 3 not shown, the CW magnetic sensor 16Xand the CCW magnetic sensor 16Y which are indicated by an imaginary lineare adhered. As shown in the drawing, the CW magnetic sensor 16X and theCCW magnetic sensor 16Y are disposed near the trajectory of rotation R,the CW magnetic sensor 16X is fixed as displaced by an angle of α0 inthe CCW direction, and the CCW magnetic sensor 16Y is fixed as displacedby an angle of α1 in the CCW direction.

Assuming that the positions of the CW magnetic sensor 16X and the COWmagnetic sensor 16Y are P1 and P2, respectively, and the centerpositions of the rotor magnetic pole portions 8a are P0 and P3, when therotor 8 rotates clockwise, a control circuit not shown receives a signalof the CW magnetic sensor 16X only and controls to excite the statormagnetic pole portion 9a which corresponds to the position P0 when theCW magnetic sensor 16X detects a magnetic flux at the position P1. Whenthe rotor 8 rotates counterclockwise, the above control circuit receivesa signal of the CCW magnetic sensor 16Y only and controls to excite thestator magnetic pole portion 9a which corresponds to the position P3when the CCW magnetic sensor 16Y detects the magnetic flux at theposition P0.

Referring to FIG. 38, the sizes of the angles α0 and α1 will bedescribed. As described above, FIG. 38 shows a difference between achange of the magnetic flux density in the outside space of the rotorend face of the brushless motor and the rotational position of the rotordetected by the magnet piece to be detected. And, the time difference Tcan be converted into a rotational angle of the rotor, and thisrotational angle is equal to the angle of lead of the magnetic flux.

In view of the above, in this embodiment, the deviated angles α0 and α1of the CW magnetic sensor 16X and the CCW magnetic sensor 16Y are set tobe substantially equal to the angle of lead of the magnetic fluxdensity.

By structuring as described above, in the brushless motor 1 of thisembodiment, when the rotor 8 rotates clockwise CW as shown in FIG. 15,the CW magnetic sensor 16X detects the magnetic flux of the magnet piece17 to be detected when the magnet piece 17 to be detected has reachedthe position P1, and the aforementioned control circuit excites thestator magnetic pole portion 9a corresponding to the position P0. Atthis time, since the peak point of the magnetic flux density in theoutside space of the rotor 8 is at the position P1, the rotor 8 can berotated most efficiently and, as a result, the motor efficiency can beimproved.

Inversely, when the rotor 8 rotates counterclockwise, the CCW magneticsensor 16Y detects the magnetic flux of the magnet piece 17 to bedetected which has reached the position P2, and the stator magnetic poleportion 9a corresponding to the position P3 is excited. Thus, the motorefficiency can be improved in the same way.

In the brushless motor 1 of this embodiment, when the rotor 8 rotatesclockwise CW as shown in FIG. 15, the CCW magnetic sensor 16Y can beused. More specifically, as described above, since the CCW magneticsensor 16Y is fixed as displaced by the angle α1 in the CCW directionwhen rotated counterclockwise CCW, when this is seen from the viewpointof rotating clockwise CW, the CCW magnetic sensor 16Y has an angle ofdelay. Therefore, when rotating CW, the CCW magnetic sensor 16Y can beused for an angle of delay. And, when rotating CCW, the CW magneticsensor 16X can be used for an angle of delay.

For carrying equipment, a bidirectionally rotatable brushless motor,which needs to let out at a low speed and at high torque when workingand to reversely rotate quickly at a high speed and at low torque whenwinding, is used. The bidirectionally rotatable brushless motor hasdifferent angles of lead of the magnetic flux density in respectiverotating directions, and is provided with one magnet piece to bedetected, a working magnetic sensor for detecting a rotational positionof the rotor when working, and a winding magnetic sensor for detecting arotational position of the rotor when winding; the working magneticsensor is fixed as displaced by an angle equal to an angle of lead ofthe magnetic flux in an opposite direction with respect to the rotatingdirection of the rotor at high torque when working, and the windingmagnetic sensor is fixed as displaced at a large angle in an oppositedirection with respect to the rotating direction (opposite rotatingdirection from when working) of the rotor at low torque when winding. Bymatching with the angle of lead of the magnetic flux at each torque ofthe working and winding magnetic sensors, a bidirectionally rotatablebrushless motor which has different rotating speed and torque, and highefficiency in each rotating direction can be obtained.

As obvious from the above description, the brushless motor of the thirdgroup of this invention has a magnet piece to be detected for specifyinga rotational position of the rotor, a CW magnetic sensor for detecting arotational position of the rotor rotating clockwise and a CCW magneticsensor for detecting a rotational position of the rotor rotatingcounterclockwise, and since the CW magnetic sensor and the CCW magneticsensor are disposed as displaced by a prescribed angle respectively inopposite directions with respect to a rotating direction of the rotor,when the rotor rotates in either direction, clockwise orcounterclockwise, the stator magnetic pole portion advanced by an angleequal to an angle of lead of the magnetic flux than the actualrotational position of the rotor can be excited. Thus, the rotor can berotated most efficiently, and a bidirectionally rotatable brushlessmotor having a high motor efficiency can be obtained.

Using the brushless motor of the second group of this invention, thebidirectional rotation like the brushless motor of the third group willbe described.

As described above, since three magnetic sensors are generally requiredfor the rotation in one direction, the bidirectionally rotatablebrushless motor uses six magnetic sensors. As shown in FIG. 16, theinventors determined the rated efficiency, maximum load and maximumrotating speed, assuming the positions of a Hall IC to be 21 mm, 23 mm,24.5 mm and 26 mm, at a position (angle of lead 0°) with the sameefficiency when rotating clockwise (CW) and counterclockwise (CCW) usingthree sensors as one set. It is seen from FIG. 16 that sensing could notbe made by the Hall IC with R24.5 mm and R26 mm. And, as shown in FIG.17, in the case of R23 mm, when the same voltage is applied to rotate CWand CCW, the motor efficiencies are different, but the rotation has lessvariation through the full range, and net properties (maximum rotatingspeed) become same. Similarly, as shown in FIG. 18, in the case of R21mm, when the same voltage is applied to rotate CW and CCW, the motorefficiencies and the rotating speeds under high load are same althoughnet properties are different.

In FIG. 17 and FIG. 18, 50%, 70% and 100% show the relation between therotating speed and the torque by duty, and the circles show the relationbetween the circuit current and the torque. In the both drawings, thesolid line indicates CCW and the dotted line indicates CW.

And, when the Hall IC is set to R23 mm, a rotating speed is fixed at1200 rpm, and torque is varied, the deviation of the peaks of themagnetic flux density outside of the rotor and the signal of the Hall ICobtained from the rotor end face at the maximum efficiency withrespective torque is as follows.

    ______________________________________               Deviation of Hall IC and    Torque     peaks of magnetic flux                              Maximum    (Kgm)      density (electrical angle)                              efficiency (%)    ______________________________________    0.05       0° ± 5°                              90    0.10       0° ± 5°                              87    0.15       0° ± 5°                              85    0.20       0° ± 5°                              82    0.25       0° ± 5°                              79    ______________________________________

It is seen from the above table that when set to R23 mm, the maximumefficiency has less change with respect to the mounting error of theHall IC in the rotating direction, and the deviated degree is sameregardless of the load, so that setting can be made under any load.

The above embodiment indicates that the arbitrary selection of thesetting position of the magnetic sensor allows to obtain a motor havingthe performance suitable for use with the structure not changed. Morespecifically, when the same maximum rotation and the same torque arerequired for both rotations of normal and reverse, the magnetic sensoris set to, for example, the above R23 mm. And, in a washing mode, like amotor used for washing machines, when the performance such as rotatingspeed of 1200 rpm, torque of 0.24 kgm and rotation in both directions isrequired, and in a spin-drying mode, when the performance such as arotating speed of 2000 rpm, torque of 0.05 kgm and rotation in onedirection is required, magnetic sensor is set to, for example, the aboveR21 mm. The above description has been made with the Hall IC changed itsposition radially, and it is to be understood that the same effect canbe obtained by adjusting the angle of lead at each R position.

It is seen from the above embodiment that it is preferable to select apattern suitable for application at a desired rotation, like the abovemotor for washing machines, from the great number of data previouslycollected with rotating directions CW and CCW under the conditions thatthe magnetic sensor had its positions changed variously. In the abovetable, the deviation of the Hall IC and the peaks of the magnetic fluxdensity is different from the table indicated in connection with thebrushless motor of the second group, because the former reflects theresults obtained by groping for conditions suitable for thebidirectional rotations of normal and reverse.

Now, devices which are used for the above brushless motors of the firstto third groups of this invention to improve their performance will bedescribed.

FIG. 19 is a view showing a magnetic sensor board. This embodiment has asensor driving power supply disposed on the magnetic sensor board 15.More specifically, a generating coil 34 is disposed on the magneticsensor board 15, the generating coil 34 is connected with an electroniccircuit 35 which is then connected with a power supply 36, and magneticsensors 16 are connected. In this magnetic sensor board 15, an a.c.current passes through the generating coil 34 due to a leaked magneticflux from the rotor, subjected to full wave rectification or half-waverectification in a rectifier circuit, has a voltage stepped up in astep-up circuit, and stored in the power supply through a controlcircuit as shown in FIG. 20. As the control circuit, one or two or morediodes are used, and the step-up circuit is disposed as required andmade of a step-up coil. When the magnetic sensor board 15 is structuredas described above, the leaked magnetic flux from the rotor can beeffectively used. And a conventionally used external power supply and anexternal wiring therefor can be eliminated. Thus, the magnetic sensorboard 15 can have high generating capacity and be formed compactincluding the magnetic sensors and the power supply. Furthermore, asshown in FIG. 21, the generating coil 34 can be also formed by windingan auxiliary coil on a tooth portion of the stator 9. For the generatingcoil 34, a sheet coil which is suitable to make it small and thin ispreferably used, and for the power supply 36, a high-capacity capacitoror a secondary battery which is rechargeable is used. In this way,generation can be made in a large volume, and via the electronic circuitpower supply, electricity can be taken out of the motor to control anexternal actuator.

And, FIG. 22 shows another embodiment which effectively uses theaforementioned leaked magnetic flux to use as the power supply forcontrolling the external actuator. In this case, a part 41, whichprotrudes toward the housing member 3 of the brushless motor 1, isdisposed on a mounting plate 40 to which the brushless motor 1 is fixed,the above generating coil 34 is attached to the leading end of the part41, and a lead 14 from the generating coil 34 is connected to a controlcircuit 42 and a battery 43. On the other hand, a hole 3a is formed inthe housing member 3 to align with the generating coil 34, and the part41 is passed through the hole 3a to set the generating coil 34 close tothe rotor end face 8b. In FIG. 22, reference numeral 44 indicates a holethrough which the rotatable shaft 7 is passed. The generating coil 34which is, for example, a sheet coil may be disposed outside of thehousing member 4 opposite from the housing member 3 which is in contactwith the mounting plate 40. Thus, the generating coil 34 can be disposedon an appropriate plate inside or outside of the motor to use theobtained power for the magnetic sensors and as a driving power for theoutside of the motor. These embodiments using the leaked magnetic fluxfrom the rotor to generate a back electromotive force can be also usedwhen the rotor is rotating by inertia.

FIG. 23 and FIG. 24 are views showing another embodiment of the magneticsensor board. Hollow portions 15c are formed in the magnetic sensorboard 15, the magnetic sensors 16 are fitted in the hollow portions 15c,and the front and back faces of the magnetic sensor board 15 are moldedwith a nonconductive resin 37 which contains a material having good heatconductivity, such as alumina material. In this structure, since thehollow portions 15c are formed in the magnetic sensor board 15,positioning of the magnetic sensors 16 can be made easily, and moldingwith the radiating resin 37 allows satisfactory radiation of themagnetic sensors. Conventionally, the magnetic sensors were mounted onthe magnetic sensor board, which therefore had an uneven surface becauseof the magnetic sensors, making it difficult to mold with a resin. But,in this embodiment, since the hollow portions 15c are formed and themagnetic sensors 16 are fitted therein, a positioning effect is providedand the board has a flat surface, making it easy to mold with a resin.Besides, a radiating effect can be obtained by molding with the resin asdescribed above.

FIG. 25 and FIG. 26 show that coils 38 are used as the magnetic sensors.FIG. 25 shows sheet coils, and FIG. 26 shows coils having toroidalwindings applied. In these cases, a back electromotive force isgenerated when the leaked magnetic flux from the rotor crosses the coils38 and used as a position detecting signal.

As described above, when the back electromotive force is used to detecta position, the position cannot be detected at the time of starting whenthe rotor remains stationary because the back electromotive force is notgenerated yet. Therefore, the control shown in FIG. 27 is conducted.Specifically, in the flowchart of FIG. 27, first, excitation is madewith a current of a limited value of a current limiter by a drive signalhaving a certain pattern for a prescribed time. Thus, the rotor moves toa position corresponding to the exciting pattern and its position isdetermined. Then, when a commutation signal is given under a state thata current is passed to switch an output pattern, the motor is rotated togenerate the back electromotive force, and the position is detected bythe coils. When such coils are used, the magnetic sensors such as a Hallelement and a Hall IC are not needed, and these coils can be producedinexpensively because a copper wire is used. And, they have advantagesthat a small number of terminals is used as compared with conventionalmagnetic sensors, they are heat resistant, and a tolerance is not strictin their production.

FIG. 28 shows that the magnetic sensor 16 is movably disposed withrespect to the rotor end face 8b. Specifically, a cylindrical body 45 isdisposed at an appropriate place within the housing members 3, 4, anonmagnetic working rod 46 is movably disposed axially in thecylindrical body 45, the magnetic sensor 16 is fixed to the working rod46 on its rotor side, and a magnet 47 is fixed to the other end of theworking rod 46. Opposing to the magnet 47, a film coil 48 is disposedoutside of the housing member to electrically conduct it. Therefore, thefilm coil 48 is excited by passing a current, the magnetism of the filmcoil 48 is changed by a controller not shown to attract or repulse themagnet 47, the magnetic sensor 16 is axially moved by the working rod 46to adjust a distance from the rotor end face 8b, and a rotation area ofthe motor is changed accordingly. FIG. 29 is a graph showing therelation between an angle of lead and a distance between the magneticsensor 16 and the rotor end face 8b when the magnetic sensor 16 is movedas described above. It is seen that when the magnetic sensor 16 movesaway from the rotor end face 8b, the angle of lead advancesproportionally from point a in the drawing. This point a wasexperimentally obtained to be a value of 1.5 times of the thickness ofthe field permanent magnet 11. And, in FIG. 30, the line indicated bythe lead line 1 shows that the magnet 47 and the film coil 48 arerepulsed to each other, or the magnet 47 is close to the rotor end face8b, and the line indicated by the lead line 2 shows that the magnet 47and the film coil 48 are attracted to each other, or the magnet 47 isaway from the rotor end face 8b than when indicated by the lead line 1.Thus, when the position of the magnet 47 is movable against the rotorend face 8b, net properties can be changed. In the invention of thefirst group, when the magnetic sensor 16 is movably disposed withrespect to the rotor end face 8b, in addition to the aforementionedeffects, positioning of the setting position of the magnetic sensor canbe facilitated in a range of a distance or below that the leakedmagnetic flux outside the rotor end face can be directly detected and adistance or more that a noise is generated in the detected signal due toan irregular magnetic flux near the rotor end face.

The above embodiments have been described assuming that a temperature isalmost constant. If the temperature condition is extremely variable whenthe motor is rotating, it is expected to use a temperature compensationmeans. And, to compensate for a temperature change, a temperature sensoris generally an essential component. Therefore, the inventors propose atechnical means to detect the motor temperature without using atemperature sensor.

Specifically, as shown in FIG. 31, a Hall voltage and a magnetic fluxdensity have a prescribed proportional relation and, as shown in FIG.32, a magnetic flux density and a temperature also have a prescribedrelation. FIG. 33 shows output voltage waveforms of the magnetic sensorwhen the rotor is rotating. It is seen that the magnetic flux densitydecreases as the magnet temperature rises, and the output voltage of themagnetic sensor lowers as the magnetic flux density decreases. Usingthese relations, or determining these relations in advance, a magneticflux density and temperature table is incorporated in the form of, forexample, a ROM in the control circuit, so that the motor temperature canbe monitored according to the output voltage of the magnetic sensor.Furthermore, a quantity of demagnetization of the rotor magnet can bealso detected according to the output voltage of the magnetic sensor. Inthe above structure, since the monitored temperature can be detectedaccording to a change in analogue output value of the magnetic sensor, adedicated temperature sensor is not required, enabling to reduce thecost. And, the demagnetization of the rotor magnet due to a temperatureincrease or unexpected phenomena can be detected according to a changein analogue output value of the magnetic sensor, so that degradation ofthe magnet performance can be seen. Besides, a temperature of the magnetbeing rotated can be directly detected without using a temperaturesensor.

In view of the fact that the magnetic sensor and the magnetic fluxdensity are influenced by a temperature as described above, thefollowing embodiment proposes a structure that the motor interior can becooled. Specifically, as shown in FIG. 34 to FIG. 36, a fan is formed.FIG. 34 and FIG. 35 show that leading ends 10b of magnetic pole portionsof a steel plate 10a of the rotor yoke 10 are bent slantingly in theform of a fan. Therefore, ventilation is made by the leading ends 10b ofthe magnetic pole portions of the steel plate 10a when the rotor isrotated, to cool the magnetic sensor. Thus, an effect by an ambienttemperature change is reduced, and a stable output voltage is attained.FIG. 36 shows that a fan 39 fixed to the rotational shaft 7 is disposedbetween the rotor end face 8b and the magnetic sensor 16. In the sameway as above, the magnetic sensor and the motor are cooled, and a stableoutput voltage can be obtained. This fan 39 is made of a nonmagneticmaterial so as not to effect on the leaked magnetic flux from the rotorend face. Therefore, the fan 39 does not cause a detection failure.

INDUSTRIAL APPLICABILITY

This invention can detect a peak point of the magnetic flux densityaround a rotor in a brushless motor which detects a rotational positionof the rotor using a magnetic sensor, and is optimum for a brushlessmotor which is required to have a high motor efficiency.

We claim:
 1. A brushless motor comprising:a housing; a rotatable shaftsupported by said housing for rotation; a rotor yoke secured to saidrotatable shaft for rotation within said housing and having a pluralityof laminated steel plates with an even number of magnetic poles formingan even number of grooves between said magnetic poles; at least one ortwo field permanent magnets inserted in every other or each of saidmagnetic poles to produce magnetic fluxes and provide at least one ortwo pairs of bridge portions between said grooves and said fieldpermanent magnets; said bridge portions being made so thin that saidbridge portions are saturated with said magnetic fluxes; at least onemagnetic sensor provided on said housing so as to face an end face ofsaid rotor yoke to detect a magnetic flux leaked into an outside of saidend face of said rotor yoke between adjacent magnetic poles; and saidmagnetic sensor being provided in an annular area between a first circlehaving a first radius equal to a first distance between a center of saidrotatable shaft and an outer surface of said field permanent magnet anda second circle having a second radius equal to a second distancebetween said center of said rotatable shaft and an outer end of saidrotor yoke so as to detect stable magnetic flux and thus provide astable motor rotation.
 2. A brushless motor according to claim 1,wherein said grooves have a bottom portion substantially aligned with atrajectory of rotation of said magnetic sensor.
 3. A brushless motoraccording to claim 1, which further comprises a nonmagnetic plateprovided between said magnetic sensor and said end face of said rotoryoke to reduce said noise.
 4. A brushless motor according to claim 1,wherein said field permanent magnets have an end face positioned insideof said end face of said rotor yoke.
 5. A brushless motor according toclaim 1, wherein said magnetic sensor is axially movable.
 6. A brushlessmotor according to claim 1, which further comprises a plurality ofcaulking sections provided in said laminated steel plates at positionsbetween said rotatable shaft and said field magnets.
 7. A brushlessmotor according to claim 1, wherein said magnetic sensor is set to scana range from said first circle to a third circle having a third radiusequal to a third distance between said center of said rotatable shaftand a middle point between said outside of said field magnets and saidouter end of said rotor yoke.
 8. A brushless motor, comprising:ahousing; a rotor yoke having a plurality of laminated steel plates withan even number of magnetic poles and rotatably supported by saidhousing; at least one or two field permanent magnets provided in everyother or each of said magnetic poles; a magnetic piece provided on anend face of said rotor yoke for use in detecting a rotational positionof said rotor yoke; clockwise and counterclockwise magnetic sensorsprovided in vicinity of a trajectory of rotation of said magnetic piecefor directly detecting rotational positions of said rotor in clockwiseand counterclockwise directions, respectively; and said clockwise andcounterclockwise magnetic sensors being displaced in counterclockwiseand clockwise directions, respectively, from the center of said magneticpoles by an angle substantially equal to a lead angle of a magneticflux, wherein said lead angle is a difference in electrical anglebetween a first peak point of a flux density in an outside space of saidrotor yoke end face where there is magnetic interaction with said statorand a second peak point of said flux density where there is no magneticinteraction with said stator.
 9. A brushless motor according to claims 1or 8, wherein a Hall IC is used for the magnetic sensor, and a distancebetween the Hall IC and the rotor yoke end face is at least larger thana thickness of the field magnet.
 10. A brushless motor according toclaims 1 or 8, wherein a Hall element is used for the magnetic sensor,and a decrease in magnetism of the rotor magnet is detected according toa relation among a Hall voltage, a magnetic flux density and atemperature.
 11. A brushless motor according to claim 10, which furthercomprising a plurality of magnetic sensors for detecting a magnetic fluxleaked outside from an end face of the rotor, provided on a plurality ofconcentric circles having different diameters according to differentangles of lead of said flux density in the outside space of said rotoryoke end face, wherein said angle of lead is a difference in electricalangle between a first peak point of said outside magnetic flux densitywhere there is magnetic interaction with said stator and a second peakpoint of said outside magnetic flux density where there is no magneticinteraction with said stator.
 12. A brushless motor according to claims1 or 8, wherein leading ends of magnetic pole portions of a steel plateof the rotor yoke are bent slantingly in the form of a fan, andventilation is made by the leading ends of the magnetic pole portions byrotation yoke of the rotor to cool the magnetic sensor.
 13. A brushlessmotor according to claims 1 or 8, wherein a generating coil is disposedon a magnetic sensor board to obtain a back electromotive force by saidcoil with the leaked magnetic flux from the rotor and the backelectromotive force is stored in a rechargeable power supply via anelectronic circuit.
 14. A brushless motor according to claim 1 or 8,wherein a generating coil is disposed on a tooth portion of the statorto obtain a back electromotive force by said coil with the leakedmagnetic flux from the rotor and the back electromotive force is storedin a rechargeable power supply via an electronic circuit.
 15. Abrushless motor according to claims 1 or 8, wherein a part, whichprotrudes toward housing of the brushless motor, is disposed on amounting plate to which the brushless motor is fixed, a generating coilis attached to said part, said housing member has a hole formed to alignwith said generating coil, and said part is passed through the hole toset said generating coil close to the rotor end face.
 16. A brushlessmotor according to claims 1 or 8, wherein a generating coil is disposedoutside said housing to obtain a back electromotive force by said coilwith the leaked magnetic flux from the rotor.